The present invention relates to a device for determining the inclination of a plane with respect to a theoretical horizontal plane.
Devices adapted to determine the horizontality of a straight line, commonly termed levels or spirit levels since spirit containing a bubble has the main role in the action of these devices, are known.
A level is essentially constituted by a glass tube supported by a frame variously shaped according to the use for which the level is intended. The tube has two etched graduations, symmetrical with respect to a center or normal point, and is almost completely filled with a liquid with extremely low internal friction; inside the tube there is, therefore, a bubble of air or even merely of saturated vapor of the liquid.
The position of the bubble with respect to the graduations provides the indication of the degree of inclination of the level; the bubble is centered when its edges are symmetrical with respect to the center.
In practice the axis of the tube must be curved and therefore it is a portion of a ring (torus); to optimize the degree of sensitivity of the level, the radius of the torus must be very large, so that in practical execution it is convenient to start with a cylindrical glass tube and provide therein, by "grinding" the glass, the required toroidal space.
Despite the fact that spirit levels have always proved their good operation even for high-precision measurements, it is evident that they require a very accurate machining of their components and therefore have high production costs, often not justified especially regarding commonly used levels. The supporting frame of the glass tube, which also defines the base line of the level, must furthermore be very strong, and therefore heavy, to protect the glass tube and to avoid deformations which would be detrimental to the accuracy of the measurement.